An irrelevant data point:
I actually found there was a decent uptick in performance of xrdcp if I turn off async reading in the server. *However*, that was for local->local transfers, so the decrease was from 600MB/s to around 500MB/s on my Mac laptop.
A relevant data point:
I found that the dCache / proxy combination worked poorly with async, and have always kept it off.
Brian
On Nov 13, 2012, at 2:22 PM, Andrew Hanushevsky <[log in to unmask]> wrote:
> Hi Matevz,
>
> Andreas is right in that you can get that effect with async reading. Though it can be avoided with a better algorithm which, unfortuantely, wasn't used. So, yes, set the cache to zero for xrdcp, though I would be interested in seeing what effect it has on transfer rate with a single source as well as multiple sources.
>
> Andy
>
> On Tue, 13 Nov 2012, Matevz Tadel wrote:
>
>> Thanks Andy, Andreas!
>>
>> Andreas told me this is a feature of async reading and that it gets sequential if one sets readcachesize to 0.
>>
>> Funny that I never printed offsets before :)
>>
>> Cheers,
>> Matevz
>>
>> On 11/13/12 10:04, Andrew Hanushevsky wrote:
>>> Hi Matevz,
>>> This is a known problem. Yes, it bizzare but it is what it is. We will have to
>>> wait for 4.0 when we deploy the new client and the new xrdcp which should solve
>>> this problem. I agree, it's a real problem.
>>> Andy
>>> On Mon, 12 Nov 2012, Matevz Tadel wrote:
>>>> Hi,
>>>> I'm testing the monitoring collector extension that is capable of storing full
>>>> access details into a root tree. Running a simple xrdcp I realized that xrdcp
>>>> first copies data at offset of 8MB and only then the beginning of the file.
>>>> t ~ time since file open
>>>> l ~ length of request
>>>> o ~ offset
>>>> // file_len=4983779
>>>> SXrdIoInfo::Dump() N_reqs = 2, N_vec_read_subreqs = 0
>>>> 0 Read t=2 l=483 o=4983296
>>>> 1 Read t=4 l=4983296 o=0
>>>> // file_len=9311384
>>>> SXrdIoInfo::Dump() N_reqs = 2, N_vec_read_subreqs = 0
>>>> 0 Read t=2 l=922776 o=8388608
>>>> 1 Read t=4 l=8388608 o=0
>>>> This is even funnier for a larger file (~400MB) ... the first 8MB (offset=0)
>>>> are read after 238MB are already read, see below, entry 60.
>>>> What's the secret here? :)
>>>> Cheers,
>>>> Matevz
>>>> // file_len=428002641
>>>> SXrdIoInfo::Dump() N_reqs = 102, N_vec_read_subreqs = 0
>>>> 0 Read t=5 l=4194304 o=8388608
>>>> 1 Read t=10 l=4194304 o=12582912
>>>> 2 Read t=20 l=4194304 o=16777216
>>>> 3 Read t=35 l=4194304 o=20971520
>>>> 4 Read t=45 l=4194304 o=25165824
>>>> 5 Read t=55 l=4194304 o=29360128
>>>> 6 Read t=65 l=4194304 o=33554432
>>>> 7 Read t=75 l=4194304 o=37748736
>>>> 8 Read t=85 l=4194304 o=41943040
>>>> 9 Read t=95 l=4194304 o=46137344
>>>> 10 Read t=105 l=4194304 o=50331648
>>>> 11 Read t=115 l=4194304 o=54525952
>>>> 12 Read t=130 l=4194304 o=58720256
>>>> 13 Read t=140 l=4194304 o=62914560
>>>> 14 Read t=155 l=4194304 o=67108864
>>>> 15 Read t=165 l=4194304 o=71303168
>>>> 16 Read t=170 l=4194304 o=75497472
>>>> 17 Read t=180 l=4194304 o=79691776
>>>> 18 Read t=190 l=4194304 o=83886080
>>>> 19 Read t=205 l=4194304 o=88080384
>>>> 20 Read t=215 l=4194304 o=92274688
>>>> 21 Read t=225 l=4194304 o=96468992
>>>> 22 Read t=240 l=4194304 o=100663296
>>>> 23 Read t=255 l=4194304 o=104857600
>>>> 24 Read t=260 l=4194304 o=109051904
>>>> 25 Read t=265 l=4194304 o=113246208
>>>> 26 Read t=275 l=4194304 o=117440512
>>>> 27 Read t=285 l=4194304 o=121634816
>>>> 28 Read t=295 l=4194304 o=125829120
>>>> 29 Read t=305 l=4194304 o=130023424
>>>> 30 Read t=315 l=4194304 o=134217728
>>>> 31 Read t=325 l=4194304 o=138412032
>>>> 32 Read t=335 l=4194304 o=142606336
>>>> 33 Read t=345 l=4194304 o=146800640
>>>> 34 Read t=360 l=4194304 o=150994944
>>>> 35 Read t=370 l=4194304 o=155189248
>>>> 36 Read t=375 l=4194304 o=159383552
>>>> 37 Read t=385 l=4194304 o=163577856
>>>> 38 Read t=390 l=4194304 o=167772160
>>>> 39 Read t=400 l=4194304 o=171966464
>>>> 40 Read t=405 l=4194304 o=176160768
>>>> 41 Read t=420 l=4194304 o=180355072
>>>> 42 Read t=425 l=4194304 o=184549376
>>>> 43 Read t=435 l=4194304 o=188743680
>>>> 44 Read t=445 l=4194304 o=192937984
>>>> 45 Read t=455 l=4194304 o=197132288
>>>> 46 Read t=465 l=4194304 o=201326592
>>>> 47 Read t=475 l=4194304 o=205520896
>>>> 48 Read t=485 l=4194304 o=209715200
>>>> 49 Read t=495 l=4194304 o=213909504
>>>> 50 Read t=505 l=4194304 o=218103808
>>>> 51 Read t=515 l=4194304 o=222298112
>>>> 52 Read t=525 l=4194304 o=226492416
>>>> 53 Read t=535 l=4194304 o=230686720
>>>> 54 Read t=540 l=4194304 o=234881024
>>>> 55 Read t=550 l=4194304 o=239075328
>>>> 56 Read t=560 l=4194304 o=243269632
>>>> 57 Read t=575 l=4194304 o=247463936
>>>> 58 Read t=580 l=4194304 o=251658240
>>>> 59 Read t=590 l=4194304 o=255852544
>>>> 60 Read t=605 l=8388608 o=0
>>>> 61 Read t=625 l=4194304 o=260046848
>>>> 62 Read t=635 l=4194304 o=264241152
>>>> 63 Read t=645 l=4194304 o=268435456
>>>> 64 Read t=655 l=4194304 o=272629760
>>>> 65 Read t=665 l=4194304 o=276824064
>>>> 66 Read t=675 l=4194304 o=281018368
>>>> 67 Read t=680 l=4194304 o=285212672
>>>> 68 Read t=690 l=4194304 o=289406976
>>>> 69 Read t=695 l=4194304 o=293601280
>>>> 70 Read t=705 l=4194304 o=297795584
>>>> 71 Read t=715 l=4194304 o=301989888
>>>> 72 Read t=730 l=4194304 o=306184192
>>>> 73 Read t=745 l=4194304 o=310378496
>>>> 74 Read t=760 l=4194304 o=314572800
>>>> 75 Read t=770 l=4194304 o=318767104
>>>> 76 Read t=780 l=4194304 o=322961408
>>>> 77 Read t=790 l=4194304 o=327155712
>>>> 78 Read t=800 l=4194304 o=331350016
>>>> 79 Read t=810 l=4194304 o=335544320
>>>> 80 Read t=820 l=4194304 o=339738624
>>>> 81 Read t=825 l=4194304 o=343932928
>>>> 82 Read t=835 l=4194304 o=348127232
>>>> 83 Read t=850 l=4194304 o=352321536
>>>> 84 Read t=855 l=4194304 o=356515840
>>>> 85 Read t=870 l=4194304 o=360710144
>>>> 86 Read t=880 l=4194304 o=364904448
>>>> 87 Read t=895 l=4194304 o=369098752
>>>> 88 Read t=905 l=4194304 o=373293056
>>>> 89 Read t=915 l=4194304 o=377487360
>>>> 90 Read t=925 l=4194304 o=381681664
>>>> 91 Read t=935 l=4194304 o=385875968
>>>> 92 Read t=940 l=4194304 o=390070272
>>>> 93 Read t=950 l=4194304 o=394264576
>>>> 94 Read t=970 l=4194304 o=398458880
>>>> 95 Read t=975 l=4194304 o=402653184
>>>> 96 Read t=985 l=4194304 o=406847488
>>>> 97 Read t=995 l=4194304 o=411041792
>>>> 98 Read t=1005 l=4194304 o=415236096
>>>> 99 Read t=1010 l=4194304 o=419430400
>>>> 100 Read t=1025 l=4194304 o=423624704
>>>> 101 Read t=1030 l=183633 o=427819008
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